As a softening agent for rubber composition, conventionally a high aromatic oil has been broadly employed as a process oil in a field of rubber composition for a pneumatic tire or others in a view point of applying high loss performance (high heat generating property) or affinity with rubber. On the other hand, in late years, instead of the aromatic oil, a process oil including less than 3% by weight of polycyclic aromatic compounds (PCA) component called as Treated Distilled Aromatic Extracts (T-DAE), Mild Extracted Solvates (MES) or so became to be employed.
Such a substitute oil, however, has lower softening point than conventional aromatic oils, and in replacing simply, temperature dependency of viscoelasticity characteristic of the rubber composition (G′, G″, tan δ) tends to shift toward low temperature side. Therefore, there was a problem that a wet skid resistant performance in an actual tire performance degrades because tan δ value at 0° C. as an indicator of wet skid performance decreases.